Safari doesn't keep past downloads in Downloads list

This problem I've been having started when the latest version of Safari moved from a Downloads window to a Downloads pop-up pane. My expectation as to how the pane should work is this: the 20 most recent downloads are shown in the list, and when a new download begins, the oldest download is removed from the list, thereby keeping the new list updated with the 20 latest downloads. My problem is that while the pane still keeps 20 past downloads listed, they're not always recent downloads. For example, when I download a file, the file will typically remain in the list until I begin a new download, at which point the slightly earlier download will be removed from the list, while even older downloads remain listed. So at the moment, listed are five recent downloads and fifteen downloads from many months ago, while downloads from days or hours ago have been removed from the list. This is incredible frustrating and unhelpful.

In Preferences I have (and always have) "Remove download list items" set to "Manually." Currently I am running the lasted versions of OSX (10.7.3) and Safari (5.1.5).

Thanks for any help